Increased airway smooth muscle (ASM) is a characteristic of severe asthma and strongly associated with airway hyperresponsiveness. Bronchial Thermoplasty (BT) aims is a new technique in which heat is applied to the airway. We hypothesize that BT causes reduced ASM in patients with severe asthma. We investigated the effect of BT on the airway in patients with severe asthma, acute effects in a pig model and the effect of hyperthermia on ASM and bronchial epithelial cells. We found a significant reduction in ASM and goblet cells at 6 weeks and 1 year post-BT, respectively. Acute effects of BT in the pig airway suggested a sterile injury pattern. Exposure to 65oC produced morphological changes in ASM and epithelial cells. We conclude that there is evidence of ASM and goblet cell reduction in response to BT but further confirmation awaits full analysis of the study in asthmatics.